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A297195
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Number of bitriangular permutations (row sums of A272644 if that triangle is prefixed with a row for n=1).
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3
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1, 1, 2, 7, 28, 133, 726, 4483, 30896, 235105, 1957930, 17712799, 172980804, 1813760317, 20323234814, 242353047355, 3064550705752, 40958281206169, 576917769130578, 8541793624670551, 132623408805525740, 2154730841214003061, 36560670776303600422, 646697046042017004787
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OFFSET
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1,3
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LINKS
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MAPLE
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if n = 1 then
1;
else
end if;
end proc:
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MATHEMATICA
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A272644[n_, m_] := Sum[StirlingS2[m+1, i+1] (-1)^(m-i) i^(n-m) i!, {i, 0, m}];
a[n_] := If[n == 1, 1, Sum[A272644[n, m], {m, 1, n-1}]];
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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